Polyamides comprise a large class of polymers having a wide range of properties. Many polyamides have excellent combinations of properties for particular applications. One important class of polyamides are the polylactams prepared by the polymerization of lactams such as caprolactam and the like. Polycaprolactam, more commonly known as nylon 6, is the most widely used of the polylactams because of its excellent mechanical and physical properties and its low cost. Because of the many desirable properties of polylactams, polylactams other than polycaprolactam have been used to a considerable extent when nylon 6 is unsuited to some specific end use. Nylon 12, manufactured from lauryllactam or 12-aminododecanoic acid, is an example of such a polymer. The foregoing polymer is characterized by lower water absorption and consequently better dimensional stability and electrical properties than nylon 6. Nylon 12 is also more flexible and lower melting than nylon 6.
For still other applications, a polyamide having a higher water absorption coupled with a higher elasticity than nylon 6 would be useful for a number of applications. Some nylon copolymers are known to provide the characteristics just mentioned. Polyamide-polyether copolymers are known to have a combination of properties making them suitable for use as fibers, fabrics, films, foams, and molded articles. It is also known that lactam-polyol copolymers can be prepared by the base catalysts of lactams in the presence of polyalkylene glycols or other polymerizable polyol intermediates using isocyanate initiators. This method of polymerization yields a block copolymer with a number of good properties at a reasonable cost. One of the principal disadvantages of the polylactam-polyether copolymers prepared by this method has been the poor heat stability of the copolymers.
Accordingly, it would be highly desirable to provide terpolymers of lactam having properties of improved heat stability and properties not anticipated by simple end-chaining of long blocks of polylactam structure onto existing polymers. It would also be desirable to modify the properties of a terpolymer in the direction of elastomeric or crystalline materials depending upon the reaction amounts of the monomeric segments utilized in the polymerization process.